A film forming process, one of the semiconductor manufacturing processes, is performed by ALD (Atomic Layer Deposition) in which a raw material gas and a reactant gas for oxidizing, nitriding or reducing the raw material gas are alternately supplied, CVD (Chemical Vapor Deposition) in which a raw material gas is decomposed in a vapor phase or made to react with a reactant gas, or the like. As for the raw material gas used in the film forming process, a sublimated gas of the raw material is used in order to extremely reduce the amount of impurities introduced into a substrate and increase a density of crystal after film formation. For example, the raw material gas is used for a film forming apparatus for forming a high dielectric film by ALD.
In such a film forming apparatus, a raw material gas is obtained by vaporizing (sublimating) a raw material by heating a raw material container in which a solid or liquid raw material is accommodated. A carrier gas is supplied into the raw material container, and the raw material is supplied into a processing chamber by the carrier gas. The raw material gas is combination of the carrier gas and a gaseous raw material. In controlling a thickness, a quality or the like of a film formed on a semiconductor wafer (hereinafter, referred to as “wafer”), it is required to accurately control an amount of the vaporized raw material (flow rate of the raw material contained in the raw material gas).
However, the amount of the vaporized raw material in the raw material container is changed by the filling amount of the raw material. When the raw material is in a solid state, the amount of the vaporized raw material is varied by non-uniform distribution of the raw material in the raw material container or by the change in the grain size or the like. Further, when the raw material is in a solid state, the temperature of the raw material container is decreased by loss of heat caused by sublimation (referred to as “vaporization” in this specification) of the raw material. Since, however, convection does not occur in the raw material container in which the solid raw material is accommodated, the distribution of the temperature in the raw material container tends to be non-uniform. Therefore, the vaporized amount of the raw material tends to be unstable.
Recently, along with the trend toward miniaturization of a wiring pattern formed on a wafer, there is required a method capable of stabilizing a film thickness or a film quality. Although the ALD method is advantageous in that a raw material gas can be supplied within a short period of time, there is still a need for a method capable of controlling a raw material supply amount to a set value.
Japanese Patent Application Publication No. 1993-305228 discloses a technique for detecting and controlling a total mass flow of a non-evaporated gas in a system to a constant level in the case of supplying a carrier gas to a liquid raw material evaporation unit and introducing a buffer gas into the system. In that case, however, differences between the flow rate meters are not considered.
In a raw material gas supply apparatus disclosed in Japanese Patent Application Publication No. 2014-145115, since a mass flow meter is calibrated by a flow rate of a carrier gas, in a state that the flow rate of the carrier gas is set to a set value by a mass flow controller, the difference between the set value of the flow rate of the carrier gas and the flow rate measured by the mass flow meter indicates the amount of the sublimated raw material in the case where the set value of the flow rate of the carrier gas is zero. Japanese Patent Application Publication No. 2014-145115 discloses a technique for obtaining an amount of the sublimated raw material gas by multiplying the difference between the set value of the flow rate of the carrier gas and the flow rate measured by the mass flow meter by a proportional coefficient. However, the object of the present disclosure is not solved by such a technique.